EMI feedthrough filter terminal assembly for human implant applications utilizing oxide resistant biostable conductive pads for reliable electrical attachments

ABSTRACT

An EMI feedthrough filter terminal assembly includes a feedthrough filter capacitor having first and second sets of electrode plates, a passageway having a first termination surface conductively coupling the first set of electrode plates, and a second termination surface exteriorly coupling the second set of electrode plates. A conductive ferrule disposed adjacent to the capacitor includes a conductive pad of an oxide resistant biostable material on a surface thereof conductively coupled to the second termination surface. A conductive terminal pin extends through the passageway in conductive relation with the first set of electrode plates, and through the ferrule in non-conductive relation. An insulator is fixed to the ferrule for conductively isolating the terminal pin from the ferrule. A hermetic seal is disposed between the insulator and the ferrule. A second conductive pad may be conductively attached to the terminal pin and to the first termination surface independently of the lead wire.

RELATED APPLICATION

This application claims priority from Provisional Patent ApplicationSerial No. 60/360,642, filed Feb. 28, 2002.

BACKGROUND OF THE INVENTION

This invention relates generally to feedthrough capacitor terminal pinsubassemblies and related methods of construction, particularly of thetype used in implantable medical devices such as cardiac pacemakers andthe like, to decouple and shield undesirable electromagneticinterference (EMI) signals from the device. More specifically, thisinvention relates to a method of providing a conductive coating on theflanges of human implantable hermetic seals for reliable EMI filterattachment, and a method of electrical connection of the feedthroughcapacitor to the feedthrough lead wires at the hermetic gold braze. Thisinvention is particularly designed for use in cardiac pacemakers(bradycardia devices), cardioverter defibrillators (tachycardia),neuro-stimulators, internal drug pumps, cochlear implants and othermedical implant applications. This invention is also applicable to awide range of other EMI filter applications, such as military or spaceelectronic modules, where it is desirable to preclude the entry of EMIinto a hermetically sealed housing containing sensitive electroniccircuitry.

Feedthrough terminal pin assemblies are generally well known in the artfor connecting electrical signals through the housing or case of anelectronic instrument. For example, in implantable medical devices suchas cardiac pacemakers, defibrillators or the like, the terminal pinassembly comprises one or more conductive terminal pins supported by aninsulator structure for feedthrough passage from the exterior to theinterior of the medical device. Many different insulator structures andrelated mounting methods are known in the art for use in medical deviceswherein the insulator structure provides a hermetic seal to prevententry of body fluids into the housing of the medical device. However,the feedthrough terminal pins are typically connected to one or morelead wires which effectively act as an antenna and thus tend to collectstray EMI signals for transmission into the interior of the medicaldevice. In the prior art devices, the hermetic terminal pin subassemblyhas been combined in various ways with a ceramic feedthrough filtercapacitor to decouple interference signals to the housing of the medicaldevice.

In a typical prior art unipolar construction (as described in U.S. Pat.No. 5,333,095), a round/discoidal (or rectangular) ceramic feedthroughfilter capacitor is combined with a hermetic terminal pin assembly tosuppress and decouple undesired interference or noise transmission alonga terminal pin. FIGS. 1-6 illustrate an exemplary prior art feedthroughfilter capacitor 100 and its associated hermetic terminal 102. Thefeedthrough filter capacitor 100 comprises a unitized dielectricstructure or ceramic-based monolith 104 having multiplecapacitor-forming conductive electrode plates formed therein. Theseelectrode plates include a plurality of spaced-apart layers of first or“active” electrode plates 106, and a plurality of spaced-apart layers ofsecond or “ground” electrode plates 108 in stacked relation alternatingor interleaved with the layers of “active” electrode plates 106. Theactive electrode plates 106 are conductively coupled to a surfacemetallization layer 110 lining a bore 112 extending axially through thefeedthrough filter capacitor 100. The ground electrode plates 108include outer perimeter edges which are exposed at the outer peripheryof the capacitor 100 where they are electrically connected in parallelby a suitable conductive surface such as a surface metallization layer114. The outer edges of the active electrode plates 106 terminate inspaced relation with the outer periphery of the capacitor body, wherebythe active electrode plates are electrically isolated by the capacitorbody 104 from the conductive layer 114 that is coupled to the groundelectrode plates 108. Similarly, the ground electrode plates 108 haveinner edges which terminate in spaced relation with the terminal pinbore 112, whereby the ground electrode plates are electrically isolatedby the capacitor body 104 from a terminal pin 116 and the conductivelayer 110 lining the bore 112. The number of active and ground electrodeplates 106 and 108, together with the dielectric thickness or spacingtherebetween, may vary in accordance with the desired capacitance valueand voltage rating of the feedthrough filter capacitor 100.

The feedthrough filter capacitor 100 and terminal pin 116 is assembledto the hermetic terminal 102 as shown in FIGS. 5 and 6. In the exemplarydrawings, the hermetic terminal includes a ferrule 118 which comprises agenerally ring-shaped structure formed from a suitable biocompatibleconductive material, such as titanium or a titanium alloy, and is shapedto define a central aperture 120 and a ring-shaped, radially outwardlyopening channel 122 for facilitated assembly with a test fixture (notshown) for hermetic seal testing, and also for facilitated assembly withthe housing (also not shown) on an implantable medical device or thelike. An insulating structure 124 is positioned within the centralaperture 120 to prevent passage of fluid such as patient body fluids,through the feedthrough filter assembly during normal use implantedwithin the body of a patient. More specifically, the hermetic sealcomprises an electrically insulating or dielectric structure 124 such asa gold-brazed alumina or fused glass type or ceramic-based insulatorinstalled within the ferrule central aperture 120. The insulatingstructure 124 is positioned relative to an adjacent axial side of thefeedthrough filter capacitor 100 and cooperates therewith to define ashort axial gap 126 therebetween. This axial gap 126 forms a portion ofa leak detection vent and facilitates leak detection. The insulatingstructure 124 thus defines an inboard face presented in a directionaxially toward the adjacent capacitor body 104 and an opposite outboardface presented in a direction axially away from the capacitor body. Theinsulating structure 124 desirably forms a fluid-tight seal about theinner diameter surface of the conductive ferrule 118, and also forms afluid-tight seal about the terminal pin 116 thereby forming a hermeticseal suitable for human implant. Such fluid impermeable seals are formedby inner and outer braze seals or the like 128 and 130. The insulatingstructure 124 thus prevents fluid migration or leakage through theferrule 118 along any of the structural interfaces between componentsmounted within the ferrule, while electrically isolating the terminalpin 116 from the ferrule 118.

The feedthrough filter capacitor 100 is mechanically and conductivelyattached to the conductive ferrule 118 by means of peripheral material132 which conductively couple the outer metallization layer 114 to asurface of the ferrule 118 while maintaining an axial gap 126 between afacing surface of the capacitor body 104, on the one hand, and surfacesof the insulating structure 124 and ferrule 118, on the other. The axialgap 126 must be small to preclude leakage of EMI. The outside diameterconnection between the capacitor 100 and the hermetic terminal ferrule118 is accomplished typically using a high temperature conductivethermal-setting material such as a conductive polyimide. It will also benoted in FIG. 5 that the peripheral support material 132 is preferablydiscontinuous to reduce mechanical stress and also allow for passage ofhelium during hermetic seal testing of the complete assembly. In otherwords, there are substantial gaps between the supports 132 which allowfor the passage of helium during a leak detection test.

In operation, the coaxial capacitor 100 permits passage of relativelylow frequency electrical signals along the terminal pin 116, whileshielding and decoupling/attenuating undesired interference signals oftypically high frequency to the conductive housing. Feedthroughcapacitors of this general type are available in unipolar (one), bipolar(two), tripolar (three), quadpolar (four), pentapolar (five), hexpolar(six) and additional lead configurations. The feedthrough capacitors (inboth discoidal and rectangular configurations) of this general type arecommonly employed in implantable cardiac pacemakers and defibrillatorsand the like, wherein the pacemaker housing is constructed from abiocompatible metal, such as titanium alloy which is electrically andmechanically coupled to the hermetic terminal pin assembly which in turnis electrically coupled to the feedthrough filter capacitor. As aresult, the filter capacitor and terminal pin assembly prevents entranceof interference signals to the interior of the pacemaker housing,wherein such interference signals could otherwise adversely affect thedesired cardiac pacing or defibrillation function.

It is well known in the art that titanium, has a tendency to formoxides, particularly at high temperature. Titanium oxide (or trioxide)is typical of the oxides that form on the surfaces of titanium. Titaniumoxide is very rugged and very stable and in fact is often used as apigment in paints due to its long-term stability. It is also aninsulator or semiconductor.

In the prior art, the attachment between the capacitor outside diametermetallization 114 and the titanium ferrule 118 is accomplished using athermalsetting conductive adhesive 132, such as a conductive polyimide.Ablestick Corporation manufactures such polyimide compounds. If theoxide layer 134 builds up sufficiently in thickness, this can form aninsulative surface which can preclude the proper operation of thefeedthrough capacitor 100 as an effective electromagnetic interferencefilter. It is essential that the capacitor ground electrode plates 108have a very low resistance and low impedance connection at RFfrequencies. This is essential so that it can perform as a proper highfrequency bypass element (transmission line) which will short outundesirable electromagnetic interference such as that caused by cellulartelephones and other emitters. If the oxide layer 134 is very thin, itcreates only a few milliohms of extra resistance. However, recentmeasurements indicate that a thicker oxide layer can create resistance(measured at 10 MHz) ranging from 750 milliohms to over 30 ohms.

In the past, this oxide layer 134 was very difficult to detect withconventional measuring instruments. Agilent Technologies has recentlyproduced a new piece of equipment known as the E4991A MaterialsAnalyzer. This materials analyzer has the capability to measureequivalent series resistance and other properties of capacitors at veryhigh frequency.

Some background in dielectric theory is required to understand theimportance of this. FIG. 7 is the schematic representation for an idealcapacitor C, which does not actually exist. In this regard, allcapacitors have varying degrees of undesirable resistance andinductance. This is explained in more detail in “A Capacitor'sInductance,” Capacitor and Resistor Technology Symposium (CARTS-Europe),Lisbon, Portugal, Oct. 19-22, 1999, the contents of which areincorporated herein.

FIG. 8 is a simplified equivalent circuit model of the capacitor. Forthe purposes of these discussions, the IR can be ignored as it is in themillions of ohms and does not significantly contribute to the capacitorequivalent series resistance (ESR). IR also has negligible effect oncapacitor high frequency performance. The inductance (ESL) can also beignored because inductive reactance for monolithic ceramic capacitors isvery low at low frequencies. Inductance for a feedthrough capacitor isvery low and can be thought of as negligible at high frequencies.Accordingly, the capacitor ESR is the sum of the dielectric loss, theohmic losses and any losses due to skin effect. However, at lowfrequency, skin effect is negligible.

Therefore, a good low frequency model for capacitor ESR is as shown inFIG. 9. At low frequency, the capacitor ESR is simply the sum of thecapacitor's ohmic and dielectric losses.

FIG. 10 illustrates a normalized curve which shows the capacitorequivalent series resistance (ESR) on the Y axis versus frequency on theX axis. This curve has been highly compressed into a U shape so that allof the important points can be illustrated on one graph. However, oneshould imagine FIG. 10 stretched out along its X axis by many times toget the true picture. The important point here is the dielectric loss isalso known as the dielectric loss tangent. The dielectric material thatis used to build the monolithic ceramic capacitor is in itself capableof producing real loss (resistance) which varies with frequency. Thedielectric resistance is very high at low frequency and drops to zero athigh frequency. This effect can be thought of as oscillations in thecrystal structure that produce heat or changes in electronic or electronspin orbits that also produce heat. No matter which dielectric model oneuses, this dielectric loss can be very significant at low frequency. Inthe EMI filter capacitor that's typically used in cardiac pacemakers andimplantable defibrillators, a capacitance value of around 4000picofarads is typical. Typical values of dielectric loss would be around4000 ohms at 1 kHz, around 6 to 12 ohms at 1 MHz, and only a fewmilliohms at 10 MHz. This clearly indicates that as one goes up infrequency the dielectric loss tends to disappear.

Since the 1960s it has been a common practice in the capacitor industryto measure capacitance and dissipation factor at 1 kHz. The dissipationfactor is usually defined as a percentage, for example, 2.5% maximum.What this means is that the dielectric loss resistance can be no morethan 2.5% of the capacitive reactance at a certain frequency (usually 1kHz). For example, if the capacitive reactance for a particularcapacitor was 80,000 ohms at 1 kHz with a 2% dissipation factor thiswould equate to 1600 ohms of resistance at 1 kHz. FIG. 10 alsoillustrates that the dielectric loss essentially goes to zero at highfrequency. For typical high dielectric constant monolithic ceramiccapacitors, anything above 10-20 MHz will be sufficiently high infrequency so that the dielectric loss is no longer a factor in thecapacitor ESR measurement. FIG. 10 also has superimposed on it anothercurve representing conductor ohmic loss which in a monolithic ceramicfeedthrough capacitor is typically on the order of 0.25 ohms to 0.75ohms. It should be pointed out that values of equivalent seriesresistance presented herein relate to only one illustrative example. Inactual fact, the ESR of the capacitor varies with the capacitance value,the number of electrode plates, and the length and width of theelectrode plates. Accordingly, a wide range of “normal” ESR readings canbe obtained for many types of capacitors. For one particular capacitor anormal ESR reading might be 0.05 ohms and for another design as much as10 ohms. The important thing is that the ESR reading and the lotpopulation represent oxide free connections that are very homogenous andthe readings are stable across the lot population.

It is also possible to detect those parts in a manufacturing lotpopulation that for one reason or another have an abnormally highresistance reading. This can be done at 1 MHz by very tightlycontrolling the maximum allowable ESR. This is being done in thepresence of relatively high dielectric loss. However, by holding a verytight screening limit it is still possible to detect such out ofpopulation part. This measurement is, of course, easier to do at 10 MHz,but also quite practical at 1 MHz.

The conductor ohmic losses come from all of the feedthrough capacitorconductor materials and connections. That would include the lead wire orcircuit trace itself, the electrical connection between the lead wireand the capacitor metallization, which might be solder or athermalsetting conductive adhesive, the interface between the capacitormetallization and the internal electrode plates, the connection from thecapacitor ground metallization to a ferrule, and the bulk resistance ofthe electrode plates themselves. Conductor ohmic loss does not vary withfrequency until skin effect comes into play. Skin effect is also shownon FIG. 10 and one can see that the resistance starts to climb at thehigher frequencies. For physically small MLC chips and feedthroughcapacitors, skin effect does not really play a role until one gets tovery high frequencies, for example, above 200 MHz.

FIG. 11 is a more detailed illustration of the dielectric loss shown byitself. At very low frequency the dielectric loss in ohms is quite highand as frequency increases, one can see that dielectric loss tends to goto zero. On this scale, the conductor ohmic losses, which are shown asmetal loss, can hardly be detected (these are only a few milliohms inthis case).

As previously mentioned, titanium oxide (or niobium or tantalum oxides)can vary in resistance from a few milliohms all the way up to 10 or even30 ohms. A recently discovered problem is that when one makesmeasurements at 1 kHz it is impossible to see the effects of theseoxides because they are hidden by the dielectric loss tangent, which canbe as high as 4000 ohms or more by itself. Trying to find a resistancethat has increased from 0.25 ohms for a titanium surface that is free ofoxide up to 2 ohms is literally impossible in the presence of 4000 ohmsof dielectric loss. The reason for this is that the dielectric loss canvary slightly from part to part (typically plus or minus 20 percent).Therefore, when one is making measurements on a manufacturing lot ofceramic EMI feedthrough capacitors for medical implant applications, thepart to part variation at 1 kHz can be as much as 100 ohms due todielectric loss tangent variation alone. Therefore, it becomes quiteimpossible to detect the presence of this undesirable oxide layer on thetitanium surface. However, the recently introduced Agilent equipment iscapable of making dielectric equivalent series resistance measurementsat 10 MHz and above. This is a high enough frequency to get rid of thedielectric loss so that one can see the ohmic loss by itself (withoutbeing hidden under the dielectric loss).

FIG. 12 is a sweep from the Agilent E4991A RF Impedance-MaterialsAnalyzer. Curve 136 illustrates the capacitor equivalent seriesresistance vs. frequency. The presence of these oxides can reduce EMIfilter performance by as much as 20 dB. Stated another way, this couldreduce EMI filtering effectiveness by a ratio of 10 to 1 or more. Thisis highly undesirable in an implantable medical device given theprevious documented clinical interactions between cellular telephonesand pacemakers. For example, it has been shown that cellular telephoneinterference can completely inhibit a pacemaker or cause it to go intoasynchronous tracking or other undesirable behavior. This can be verydangerous even life threatening for a pacemaker-dependent patient.Further compounding this concern is the recent introduction throughoutthe marketplace of cellular telephone amplifiers.

One example of this is in the off shore marine boating environment.Until recently maritime communications were primarily limited to the VHFradio. However, many boaters are now relying on cellular telephones fortheir communication. Accordingly, a number of companies have introducedcellular telephone amplifiers which boost cellular telephone output from0.6 watts maximum to 3 watts. In addition, high gain marine antennas arebeing manufactured which can be anywhere from 4 to 8 feet long. Theseprovide an additional 9 dB of gain in the extreme case. Passengers onthese boats are being subjected to much higher field intensities thanwere previously contemplated by the FDA.

Another area where cellular telephone amplifiers are becomingincreasingly popular is for wireless Internet connections for lap topcomputers. It is now possible to buy small black box devices that pluginto the wall and also plug into the cellular telephone. These devicesthen plug into the lap top computer. This boosts the cellular telephoneoutput to 3 watts and also provides a high gain antenna all of which siton a desk top right in front of the operator. There are also remotecredit card scanning devices that operate under similar principles. Inshort, the public is increasingly being exposed to higher levels ofelectromagnetic fields.

Accordingly, there is an urgent and present need for EMI filteredterminals for implantable medical devices that will not only maintaintheir present performance (by not degrading in the presence of oxides)but also increase in their performance. Co-bonded ferrite slabs arebeing contemplated in order to further increase filter performance inconjunction with the principles outlined here. This will allow futurecapacitor connections with very low ESR and very low potential foroxidation at attachment points. In addition, the additional ferrite slabwill change it from a single element EMI filter to a double EMI filter(L filter). Accordingly, increased performance at cellular phonefrequencies offered thereby providing complete immunity to theaforementioned new signal amplifiers. Returning to FIG. 12 one can seefrom the resistance curve 136 that at the far left hand side of thesweep (1) at 1 MHz, the resistance is approximately 6 ohms. This meansthat there is a significant, but small amount of dielectric losstangents still present at 1 MHz (the dielectric loss tangent at 1 kHz is1800 ohms). However, when one goes up to marker (2), which is at 10 MHz,we're at a point where the dielectric loss tangent has all butdisappeared. At this point, we are primarily seeing the true ohmiclosses of the device. The device measured in FIG. 12 has no titaniumoxide build-up. Accordingly, at marker (2) we have a very low resistancemeasurement of 234.795 milliohms (0.234 ohms).

FIG. 13 is the same as the sweep in FIG. 12 except this is taken from apart that has a substantial amount of undesirable titanium oxidebuild-up. Curve 136 illustrates that at marker (2) there is 23.2529 ohmsof resistance present. FIG. 13 clearly illustrates that there is enoughtitanium oxide build-up to create 23.2529 ohms of series resistance at10 MHz (a normal reading is 0.234 ohms for this particular capacitor).This is highly undesirable because it will preclude the proper operationof an EMI filter at this frequency and frequencies above.

FIGS. 14-19 illustrate a prior art rectangular bipolar feedthroughcapacitor (planar array) 200 mounted to the hermetic terminal 202 of acardiac pacemaker in accordance with U.S. Pat. No. 5,333,095.Functionally equivalent parts shown in this embodiment relative to thestructure of FIGS. 1-6 will bear the same reference number, increased by100.

As illustrated in FIGS. 14-19, in a typical broadband or low pass EMIfilter construction, a ceramic feedthrough filter capacitor, 200 is usedin a feedthrough assembly to suppress and decouple undesiredinterference or noise transmission along one or more terminal pins 216,and may comprise a capacitor having two sets of electrode plates 206 and208 embedded in spaced relation within an insulative dielectricsubstrate or base 204, formed typically as a ceramic monolithicstructure. One set of the electrode plates 206 is electrically connectedat an inner diameter cylindrical surface of the capacitor structure 200to the conductive terminal pins 216 utilized to pass the desiredelectrical signal or signals (see FIG. 16). The other or second set ofelectrode plates 208 is coupled at an outer edge surface of thecapacitor 200 to a rectangular ferrule 218 of conductive material (seeFIG. 18). The number and dielectric thickness spacing of the electrodeplate sets varies in accordance with the capacitance value and thevoltage rating of the capacitor 200.

In operation, the coaxial capacitor 200 permits passage of relativelylow frequency electrical signals along the terminal pins 216, whileshielding and decoupling/attenuating undesired interference signals oftypically high frequency to the conductive housing. Feedthroughcapacitors 200 of this general type are available in unipolar (one),bipolar (two), tripolar (three), quadpolar (four), pentapolar (five),hexpolar (6) and additional lead configurations. Feedthrough capacitors200 (in both discoidal and rectangular configurations) of this generaltype are commonly employed in implantable cardiac pacemakers anddefibrillators and the like, wherein the pacemaker housing isconstructed from a biocompatible metal such as titanium alloy, which iselectrically and mechanically coupled to the hermetic terminal pinassembly which is in turn electrically coupled to the coaxialfeedthrough filter capacitor. As a result, the filter capacitor andterminal pin assembly prevents entrance of interference signals to theinterior of the pacemaker housing, wherein such interference signalscould otherwise adversely affect the desired cardiac pacing ordefibrillation function.

FIG. 15 illustrates an unfiltered hermetic terminal 202 typical of thatused in medical implant applications. The ferrule 218 is typically madeof titanium or other biocompatible material. An alumina insulator 224 orother insulative material such as glass or the like, is used toelectrically isolate the leads 216 from the conductive ferrule while atthe same time providing a hermetic seal against body fluids. In the caseof an alumina insulator, the lead wires or leads 216 are installed intothe insulating material 224 typically by gold brazing. A gold braze isalso formed between the alumina 224 and the ferrule 218. In someapplications, this can also be done with sealing glass so that the goldbrazes are not required. The reference numbers 228 and 230, on the onehand, and 228′ and 230′, on the other (FIG. 19), show gold brazes in twoalternate locations that are used to form the hermetic seal between thetitanium ferrule 218 and the alumina insulator 224.

FIG. 18 illustrates the capacitor 200 mounted to the hermetic terminal202 of FIG. 15. The attachment 232 between the capacitor groundmetallization 214 and the titanium ferrule 218 is typically done with aconductive thermalsetting polymer, such as conductive polyimide or thelike. It is also required that an electrical/mechanical connection bemade between the capacitor inside diameter holes 212 and the four leadwires 216. This is shown at 244 and can be accomplished with athermalsetting conductive adhesive, solder, welding, brazing or thelike.

FIG. 19 is a cross-sectional view of the capacitor assembly of FIG. 18,which is typical of prior art capacitors shown in U.S. Pat. No.5,333,095 and related patents. In FIG. 19, one can see the undesirableoxide layer 234. This oxide layer can actually coat all surfaces of thetitanium ferrule (for simplicity, it is only shown on FIG. 19 in thearea where the conductive polyimide attachment 232 is made to thecapacitor ground termination 214). The thermalsetting conductivematerial 232 connects between the capacitor ground metallization 214 andthe ferrule 218. However, if there is an insulative titanium oxide layer234 as shown, this can preclude the proper operation of the feedthroughcapacitor 200 as previously mentioned.

From the foregoing it is seen that titanium housings, casings andferrules for hermetic seals are commonly used in the medical implantindustry. Pacemakers, implantable defibrillators, cochlear implants andthe like, all have ferrules or housings made of titanium. All of theaforementioned devices are also subject to electromagnetic interference(EMI) from emitters that are commonly found in the patient environment.These include cell phones, microwave ovens and the like. There are anumber of prior art patents which describe EMI feedthrough filters whichmake the implantable devices immune to the effects of EMI.

The presence of oxides of titanium can preclude the proper performanceof monolithic ceramic EMI feedthrough filters. The titanium oxides thatform during manufacturing processes or handling form a resistive layer,which shows up at high frequency. High frequency impedance analyzerplots of resistance vs frequency illustrate that this effect isparticularly prominent above 10 MHz. There is a significant need,therefore, for a novel method of providing a conductive coating on theferrules of human implantable hermetic seals for reliable EMI filterattachment. Further, there is a need for a novel method of electricalconnection of feedthrough capacitor lead wire inside diametertermination directly to the gold termination or other similarly capablematerial of hermetic seals and corresponding lead wire(s). The presentinvention fulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

The present invention resides in an EMI feedthrough filter terminalassembly which utilizes oxide resistant, biostable conductive pads, forexample gold or the like, for reliable and stable electricalattachments. Broadly, the EMI feedthrough filter terminal assemblycomprises a feedthrough filter capacitor, a conductive ferrule, aconductive terminal pin, and an insulator that is fixed to the ferrulefor conductively isolating the terminal pin from the ferrule.

More particularly, the feedthrough filter capacitor includes first andsecond sets of electrode plates, a passageway therethrough having afirst termination surface conductively coupling the first set ofelectrode plates, and a second termination surface which exteriorlycouples the second set of electrode plates. The conductive ferrule isdisposed adjacent to the feedthrough filter capacitor and has a noblemetal pad on a surface thereof which is conductively coupled to thesecond termination surface. At least one conductive terminal pin extendsthrough the passageway in conductive relation with the first set ofelectrode plates. The terminal pin also extends through the ferrule innon-conductive relation. An insulative washer is sometimes disposedbetween the feedthrough filter capacitor and the insulator.

In illustrated embodiments of the present invention the terminalassembly includes means for hermetically sealing passage of the terminalpin through the ferrule. The ferrule and the insulator comprise apre-fabricated hermetic terminal pin sub-assembly.

The second termination surface may comprise a plurality of secondtermination surfaces. In such case, an oxide resistant conductivehermetic seal includes a corresponding plurality of pads of oxideresistant conductive biostable material, conductively coupled to theplurality of second termination surfaces. Conductive connectors extendbetween the respective sets of second termination surfaces andconductive pads. The conductive pads of oxide resistant biostablematerial, typically comprise gold bond pads that may be associated witha titanium/molybdenum base. The conductive connectors are typicallytaken from the group consisting of conductive polyimide or solder.

The first passageway through the feedthrough filter capacitor maycomprise a plurality of first passageways each having a distinct firsttermination surface which is conductively coupled to a distinct firstset of electrode plates. In such case, the at least one conductiveterminal pin comprises a terminal pin extending through each of theplurality of first passageways.

A second conductive pad of an oxide resistant biostable material may beconductively attached to the lead wire. Means are then provided forconductively coupling the second conductive pad to the first terminationsurface independently of the lead wire. Such structure utilizesconductive pads of oxide resistant biostable material, for reliableelectrical attachments to both the first and second sets of electrodeplates.

An insulative washer may be disposed between the feedthrough filtercapacitor and the insulator. When the second conductive pad is providedwhich is conductively attached to the at least one lead wire, the washerincludes a gap adjacent to the terminal pin.

Preferably, the EMI feedthrough filter terminal assembly is specificallyconstructed for medical implant applications including cardiacpacemakers, implantable cardioverter defibrillators, cochlear implants,neuro-stimulators, implantable drug pumps and the like.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a top and side perspective view of a typical unipolar ceramicdiscoidal feedthrough capacitor;

FIG. 2 is an enlarged sectional view taken generally along the line 2—2of FIG. 1;

FIG. 3 is a horizontal section taken along the line 3—3 of FIG. 2,illustrating the configuration of the ground electrode plates within thecapacitor;

FIG. 4 is a horizontal section taken generally along the line 4—4 ofFIG. 2, illustrating the configuration of the active electrode plateswithin the capacitor;

FIG. 5 is a perspective view of the capacitor of FIGS. 1-4, mounted to atypical hermetic terminal;

FIG. 6 is an enlarged sectional view taken generally along the line 6—6of FIG. 5;

FIG. 7 is a schematic representation of an ideal capacitor;

FIG. 8 is a simplified equivalent circuit model for a real capacitor;

FIG. 9 is a schematic illustrating a low frequency model for capacitorESR;

FIG. 10 is a graph illustrating normalized curves which show thecapacitor equivalent series resistance (ESR) on the y axis, versusfrequency on the x axis;

FIG. 11 is a graph illustrating dielectric loss versus frequency;

FIG. 12 is a graph illustrating capacitor equivalent series resistanceversus frequency as illustrated in a sweep from an Agilent E4991Amaterials analyzer;

FIG. 13 is a graph similar to that shown in FIG. 12, illustrating theresistance in a feedthrough filter capacitor assembly when a substantialamount of titanium oxide is present on the ferrule;

FIG. 14 is a perspective view of a rectangular broadband or low pass EMIfilter capacitor;

FIG. 15 is a perspective view of a prior art unfiltered hermeticterminal typical of that used in medical applications;

FIG. 16 is a horizontal section taken generally along the line 16—16 ofFIG. 14, illustrating the configuration of active electrode plateswithin the capacitor;

FIG. 17 is a horizontal section taken generally along the lines 17—17 ofFIG. 14, illustrating the configuration of a set of ground electrodeplates within the capacitor;

FIG. 18 illustrates the capacitor of FIG. 14 mounted to the hermeticterminal of FIG. 15;

FIG. 19 is an enlarged sectional view taken generally along the line19—19 of FIG. 18;

FIG. 20 is a hermetic terminal similar to that illustrated in FIG. 15,but modified in accordance with features of the present invention;

FIG. 21 is a perspective view similar to FIG. 18, illustrating arectangular feedthrough capacitor mounted to the hermetic terminal ofFIG. 20;

FIG. 22 is an enlarged sectional view taken generally along the line22—22 of FIG. 21;

FIG. 23 is a perspective view of a surface mount round quadpolarfeedthrough capacitor embodying the present invention;

FIG. 24 is an enlarged sectional view taken generally along the line24—24 of FIG. 23;

FIG. 25 is a chart illustrating the mechanical properties ofthermoplastic polyimide supported tape adhesive;

FIG. 26 is a sectional view similar to FIG. 24, illustrating a prior artfeedthrough filter capacitor terminal typical of that shown in U.S. Pat.No. 4,424,551;

FIG. 27 is a sectional view similar to FIGS. 24 and 26, illustrating analternative embodiment of a prior art feedthrough filter capacitorterminal;

FIG. 28 is a sectional view similar to FIGS. 26 and 27, and furtherillustrating application of the present invention;

FIG. 29 is an enlarged view of the area indicated by the number 29 inFIG. 28;

FIG. 30 is an enlarged view of the area indicated by the number 30 inFIG. 28;

FIG. 31 is a perspective view of an internally grounded bipolarrectangular feedthrough capacitor as illustrated and described in U.S.Pat. No. 5,905,627;

FIG. 32 is a perspective view of a hermetic terminal suitable for usewith the internally grounded feedthrough capacitor of FIG. 31;

FIG. 33 is a sectional view through the capacitor of FIG. 31,illustrating the active electrode plates;

FIG. 34 is a sectional view similar to FIG. 33, illustrating theconfiguration of the ground electrode plates;

FIG. 35 is a perspective view of the internally grounded bipolarfeedthrough capacitor of FIG. 31 mounted to the hermetic feedthroughterminal of FIG. 32;

FIG. 36 is a cross-sectional view taken generally along the line 36—36of FIG. 35;

FIG. 37 is a perspective view of a hybrid capacitor which has thecharacteristics of a conventional surface-mounted feedthrough capacitorand an internally grounded capacitor;

FIG. 38 is a horizontal section through the capacitor of FIG. 37,illustrating the configuration of the ground electrode plates therein;

FIG. 39 is a horizontal section similar to FIG. 38, illustrating theconfiguration of the active electrode plates therein;

FIG. 40 is a perspective view of an hermetic terminal designed for usein connection with the capacitor illustrated in FIGS. 37-39, theterminal including a titanium ferrule;

FIG. 41 is a top plan view of the capacitor of FIG. 37 mounted to thehermetic terminal of FIG. 40;

FIG. 42 is a sectional view taken generally along line 42—42 of FIG. 41;

FIG. 43 is a sectional view similar to FIG. 42, illustrating a hybridcapacitor which has a centered ground pin and which is also grounded atits right and left ends to gold bond pads;

FIG. 44 is an enlarged, perspective and partially exploded view of oneof the terminal pins shown in FIG. 43;

FIG. 45 is a sectional view similar to FIG. 43, illustrating aninternally grounded hex polar capacitor and related hermetic terminalembodying the present invention;

FIG. 46 is an enlarged perspective view of a terminal pin utilized inthe structure of FIG. 45;

FIGS. 47A-C are an enlarged fragmented and sectional views of the areaindicated by the line 47 in FIG. 45, illustrating three differentembodiments of attachment of the lead wire;

FIG. 48 is a sectional view similar to FIGS. 43 and 45, illustrating anexternally grounded quadpolar device; and

FIG. 49 is an enlarged fragmented view of the area 49 shown on FIG. 48.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Titanium housings, casings and ferrules for hermetic seals are commonlyused in the medical implant industry. Pacemakers, implantabledefibrillators, cochlear implants and the like, all have ferrules orhousings made of titanium or titanium-ceramic composite structures. Allof the aforementioned devices are also subject to electromagneticinterference (EMI) from emitters that are commonly found in the patientenvironment. These include cell phones, microwave ovens and the like.There are a number of prior art patents which describe EMI feedthroughfilters which make the implantable devices immune to the effects of EMI.

The inventors have noted that the presence of oxides of titanium canpreclude the proper performance of monolithic ceramic EMI feedthroughfilters. The titanium oxides that form during manufacturing processes orhandling form a resistive layer. High frequency impedance analyzer plotsof resistance vs frequency illustrate this effect is particularlyprominent above 10 MHz. The novel invention as described herein depositsan oxide resistant conductive coating on the surface of the titanium toprovide a resistively stable area to which the ground electrode platesof the feedthrough capacitor can be reliably and consistently attached.Attachments between the capacitor ground electrode plates are typicallyperformed in the prior art by a conductive termination layer which is apart of the feedthrough capacitor, wherein the termination layerconnects the ground electrode plates in parallel. The terminationmaterial as described in the prior art provides a convenient electricaland solderable connection to the capacitor ground electrode plates. Theactive electrode plates are similarly terminated at their insidediameter (feedthrough holes).

The primary role of the EMI filter capacitor is to appear as a very lowimpedance at RF frequencies. The presence of resistance due to atitanium oxide in the capacitor connection undesirably raises itsoverall impedance. Oxides of titanium are additionally problematic inthat they are not stable with time and temperature (they can continue tobuild-up). These oxides can preclude the proper filtering function ofthe capacitor. For example, the presence of 23.25 ohm titanium oxide(s)resistance overwhelms the impedance of the feedthrough capacitor, whichgenerally measures less than 600 milliohms at the HF frequency band.This means that the feedthrough capacitor is no longer an effective EMIfilter.

The reason that EMI filters are placed at the point of lead ingress inimplantable medical devices such as cardiac pacemakers, implantabledefibrillators and the like, is to be sure that the implanted electronicdevice will continue to operate properly in the presence ofelectromagnetic fields. A notorious example is the microwave oven. Itwasn't that many years ago that a number of serious interactions weredocumented between microwave ovens and cardiac pacemakers and warningsigns appeared in stores and other places that were using such devices.The titanium housing that encompasses modern implantable devices largelyprecludes problems from microwave ovens along with effective EMIfilters. Another notable example is the cellular telephone (and otherhand held wireless communication devices). Extensive testing by the FDA,by Mount Sinai Medical Center, by Oklahoma University, the Mayo Clinicand other institutions has documented serious interactions betweencellular telephones and cardiac pacemakers and implantabledefibrillators. In implantable defibrillators, inappropriate therapydelivery has been documented. This means that the defibrillator deliversa painfully high voltage shock where it is not necessary to cardiovertthe heart. In this case the implantable defibrillator has confusedelectromagnetic interference with a chaotic ventricular rhythm. EMIfilters that properly decouple these signals provide the degree ofpatient safety that is required. However, if the filter performancedegrades in the presence of the oxides as mentioned, then the patient isclearly at risk. This means that the elimination of these oxides isessential to eliminate a serious public safety concern.

The connection between the capacitor ground termination and the titaniumferrule is typically done using a thermalsetting conductive materialsuch as a conductive polyimide material or the like. The reason for thisis that titanium is not solderable. The use of conductive thermalsettingmaterials to make this connection is well known in the art.

The novel conductive coating of the titanium ferrule of the hermeticseal as described herein is accomplished in one of a variety of ways:

1. Deposition of gold braze material in selected areas of the flangethat line up with the capacitor ground electrode terminations.Accordingly, electrical connection between capacitor termination and thegold braze material can still be accomplished as described in the priorart using the conductive polyimide. A novel feature of the invention isthat said connection is now achievable with conventional solderingprocesses.

2. Physical vapor deposition, e.g. sputtering of various materials suchas gold or platinum, and various other conductively joinable materialsonto the titanium surface.

3. Selected electroplating of gold, platinum, or other materials on thetitanium flange for the purposes of facilitating the capacitor groundelectrode connection.

4. Plasma arc deposition

5. Ion beam

6. Chemical vapor deposition

7. Laser ablation

8. Or any other deposition method that will achieve the end resultdescribed.

It should be apparent to those skilled in the art that the techniquesdescribed herein are also applicable to other hermetic seal ferrulematerials like niobium, tantalum, and the like. The present invention isalso applicable to a variety of other hermetic seal applications as usedin oil well logging, aerospace, military and other applications.

A related invention is also shown in the accompanying drawings. This isthe unique capability of connecting directly between the lead wire andthe gold braze. This is of great advantage for lead materials that formheavy oxide layers, are non-solderable, or both. For biomedicalapplications, this allows the use of titanium, niobium, tantalum andother lead materials which are much less expensive than the currentplatinum or platinum-iridium leads.

In the following description, elements of the feedthrough filtercapacitor assemblies described herein which are functionally equivalentto one another and to the feedthrough filter capacitor assemblies ofFIGS. 1-6 and 14-19 described above, will retain common referencenumbers, but increased in increments of 100.

FIG. 20 illustrates a hermetic terminal 302 which is similar to thehermetic terminal 202 of FIG. 15, but which has been modified inaccordance with the present invention by extending a gold braze area 346to create a rectangular pad as shown. The gold braze 346, which runsaround the alumina insulator 324, is also run into two pockets that areconvenient for capacitor mounting.

FIG. 21 shows a quadpolar feedthrough capacitor 300 (which is identicalto the capacitor 200 of FIG. 14) mounted to the hermetic terminal ofFIG. 20. As one can see in FIG. 21, the conductive polyimide material332 now connects between the capacitor metallization 314 and the goldbraze area 346. The gold braze forms a metallurgical bond with thetitanium and precludes any possibility of an oxide forming. Gold is anoble metal that does not oxidize and remains very stable even atelevated temperatures. The novel construction methodology illustrated inFIG. 21 guarantees that the capacitor ohmic losses will remain verysmall at all frequencies.

FIG. 22 is a cross-section of the capacitor shown in FIG. 21. One cansee that the gold braze (or weld) areas 328 and 330 that form thehermetic seal between the alumina insulator 324 and the titanium ferrule318 are desirably on the feedthrough capacitor side. This makes it easyto manufacture the gold bond pad area 346 for convenient attachment ofthe conductive thermalsetting material 332. In other words, by havingthe gold braze hermetic seals on the same side as the gold bond padarea, these can be co-formed in one manufacturing operation in a goldbraze vacuum furnace. Further, a unique thermalsetting material 348 isdisposed between the capacitor 300 and the underlying hermetic terminal302.

Another feature of the present invention is that in the prior art onlyconductive thermalsetting materials could be used to electricallyconnect the capacitor ground metallization 314 to the ferrule 318. Thisis because titanium, niobium, tantalum and other biocompatible materialsused for human implant ferrules are generally not solderable. With thepresent invention, it is now possible to replace the thermalsettingconductive adhesive with solder. Solder paste could also be used. Thisis because solder will properly wet and bond to the gold braze area 346.Solder reflow operations tend to be more cost efficient (moreautomatable) as compared to dispensing of thermalsetting conductiveadhesives. It should also be noted that the gold bond pad area 346 ofFIG. 21 could be achieved using other methods. Gold brazing is onemethod that has already been described. However, sputter coatings ofmaterial surfaces such as gold, platinum or other conductive materialscould be done. In addition, the gold bond pad area 346 could be done byelectroplating of a suitable material that would form an electrical bondto the titanium and preclude oxide formation or by any other depositionmethod capable of achieving the desired result.

Accordingly, it will be understood that a novel feature of the presentinvention is the capability of producing a hermetic seal using noblematerials such as gold braze while at the same time forming a gold bondpad or landing area to which to connect the capacitor groundmetallization. With specific reference to FIG. 22, the hermetic seal 330forms a hermetic braze connection between the ferrule 302 and thealumina insulator 324. This also, at the same time, forms the gold bondpad 346 for convenient connection of the conductive polyimide 332. Theconductive polyimide forms the electrical connection between thecapacitor ground electrode plates through the capacitor metallization314 which connects directly to the conductive polyimide 332 and to goldbond pad 346.

There are a number of advantages in having the hermetic connection 330be co-formed with gold bond pad 346. First of all there is a verysignificant manufacturing advantage to having this all done in oneoperation. A single gold pre-form can be used, which is formed toaccommodate the area as shown. In addition, this can all be done in onebatch of product put into the vacuum gold brazing furnace at one time.In a typical manufacturing operation of the hermetic terminal, batchesof parts are placed into carbon/graphite holding/alignment fixturescalled boats, the lead wires and alumina and gold pre-forms along withthe ferrules are then all loaded into this special fixture. The operatorthen places these in a sealed chamber known as a vacuum brazing furnace.Then over a period of time, the temperature is raised sufficiently tore-flow the gold braze material. The gold makes a connection betweensputtering, which was formerly placed on the alumina terminal 324 sothat good wetting takes place, and a hermetic seal is formed. There isalso a good wetting to the titanium such that a hermetic seal is formedthere also. This can all be done in one continuous operation wherein thegold only wets to the titanium in the selected areas where theconductive polyimide 332 is to be placed. Accordingly, the structure asshown in 332 in FIG. 22 can all be formed in one manufacturing step withvery little added cost. There is also an electrical advantage to doingit this way. By extending the gold bond pad over the greater area toinclude the hermetic seal portion of the gold braze, there is additionalcontact area of the gold to the titanium thereby further lowering thecontact resistance related to the formation of oxides as previouslymentioned herein. It has been demonstrated that the formation of theseoxides can reduce the effectiveness of an EMI filter at high frequency.This is because the titanium oxide would increase the capacitor'sequivalent series resistance thereby adding an undesirable resistance inseries with the bypass capacitor.

Speaking specifically to U.S. Pat. No. 5,867,361 (Wolf, et al) datedFeb. 2, 1999, FIG. 1 of the Wolf patent discloses a gold braze 40 forconnection of the conductive polyimide 47 to the titanium ferrule. Wolfindicates that the insertion loss or high frequency performance of theEMI filter is improved by connection to this gold bond pad. FIG. 9illustrates the attenuation in decibels with and without a gold bond pad40. In the Wolf patent, the hermetic seal is made between the aluminainsulator using a gold braze shown in FIG. 1 as Item 15. The gold braze15 connects between the ferrule 93 and the alumina insulator 25. Thereis also a hermetic and electrical connection made between the lead wire29 and the alumina insulator through gold braze 90. It is significantthat the entire hermetic seal is formed in this lower region of FIG. 1.The attachment to the filter capacitor 50 is made using conductivepolyimide 47 which is attached to the ferrule 93 by way of the goldbrazed material 40. In the Wolf patent, the gold braze material is anarea completely separate and distinct from the gold braze material 15which is used to form the hermetic seal. Accordingly, this is done intwo operations or two steps involving two separate gold brazedpre-forms. There is no hermetic seal between the ceramic capacitor 50and the ferrule 93. In fact, any material used to make electricalconnection between the ceramic capacitor and the ferrule is described asa conductive thermalsetting material, such as a silver filled polyimideor a solder or the like. None of these are suitable biocompatiblesealing materials for human implant applications and they certainly donot make a hermetic seal (nor does solder since it is not considered abiocompatible material).

It is a novel feature of the present invention, as shown in FIG. 22,that the hermetic seal and the gold bond pad is integrated into a singlemonolithic structure.

FIG. 23 illustrates a surface mounted quadpolar feedthrough capacitor400. A gold braze bond pad area 446 has been added to facilitate theconnection between the capacitor outside diameter metallization 414 andthe titanium ferrule 418. As mentioned before, this connection can bemade as in the past with a thermalsetting conductive adhesive 432 orwith solder or the like.

FIG. 24 is a cross-section of the quadpolar feedthrough filter capacitorterminal of FIG. 23. The gold braze area 446 or optionally 446′ has beenextended and widened so that the capacitor outside diameter electricalconnection 432 will touch off between the capacitor outside diametermetallization 414 and the gold braze surfaces 446 or 446′. By having anelectrically conductive metallurgical joint directly between thecapacitor metallization and the gold braze, there is no chance for anytitanium oxide build-up to affect the capacitor's performance.

Another inventive concept illustrated in FIG. 24 is the electricalconnection 444 between the lead wires 416 and the capacitormetallization 410 and gold braze 428, 428′. This has been made possibleby use of a thermalsetting insulative material 448.

A unique design constraint affecting filtered hermetic terminals forimplantable medical devices is that these devices are designed to bewelded into the overall titanium housing of a pacemaker, implantabledefibrillator or the like. Accordingly, the feedthrough capacitorassembly is subjected to a great deal of heat and thermal stress. Thus,the insulative material 448 has to withstand very high temperature. Onesuch insulative material 448 is a unique thermal plastic polyimidesupportive tape (coated with thermalsetting adhesive) manufactured byAblestik Electronic Materials and Adhesives, (the mechanical propertiesof which are listed in FIG. 25.) This material, which is known asAbleloc 5500, is unique in that it has the high temperaturecharacteristics of a polyimide and yet will not flow. In other words, itstays in place, which allows one to form the novel structure shown at448.

It is very important that the bottom or the surface between thecapacitor 400 and the alumina insulator 424 be sealed so that conductivematerials or fluids cannot run between the capacitor pins and short itout. The Ableloc 5500 is ideal in that it forms a seal while remainingin place. This means that for the first time the present invention canguarantee that the capacitor inside diameter connection can be betweenthe capacitor metallization 410 and the gold braze 428 or 428′, whichopens up entirely new possibilities. For the first time niobium ortantalum pins can be utilized, without preparatory and secondaryprocessing operations which are required because these materials arenotoriously covered with oxide. No longer must there be a directconnection between the capacitor metallization 410 and the pin 416itself. Instead, the gold braze 428 or 428′, which forms the hermeticseal, makes an oxide free metallurgical and very low resistanceconnection to the pin itself (in a one step operation). Accordingly, theelectrical connection 444 between the pin 416 as shown in FIG. 24 isactually from the capacitor inside diameter metallization 410 directlyto the gold braze 428. The presence of oxides on the pin simply doesn'tmatter since a very low resistance electrical connection has alreadybeen formed. This electrical connection is also RF tight allowing thefeedthrough capacitor to operate at very high frequency as a proper EMIfilter.

FIG. 26 represents a prior art feedthrough capacitor 500 typical of U.S.Pat. No. 4,424,551 and related patents. The bottom surface of thecapacitor 500 has been flooded with a nonconductive epoxy 550. Asexemplified in U.S. Pat. No. 4,424,551, the insulative material 550 iscured so that the capacitor 500 is bonded into the case 518. Subsequentto this, the entire surface above the capacitor 500 is flooded withconductive polyimide material 532, which is then centrifuged into place.It is very important during the centrifuge operation that material notflow underneath the capacitor thereby forming a short between theferrule and the capacitor inside diameter pin 516. An optionalinsulative epoxy coating 552 could be added to cosmetically cover thesurface of the capacitor 500 and offer it some degree of mechanicalprotection. As can be seen in this prior art assembly, there is no wayfor the conductive polyimide 544 at the inside diameter to reach thegold braze 528. Also, it is not possible for the outside diameterconductive polyimide 532 to reach the gold braze 530. This type of priorart assembly is sensitive to any type of titanium oxide build-up thatmay occur on the inside diameter of the titanium ferrule.

FIG. 27 illustrates another prior art feedthrough capacitor 600 andrelated structure. This unit has a substantial oxide layer 634 on theinside of the titanium ferrule 618. For simplicity, this oxide layer isonly shown on the inside diameter of the ferrule 618 where theelectrical connection to the capacitor ground metallization 614 is made(in actual practice, the oxide would to some degree coat all of theferrule surfaces). Accordingly, there will be a high resistance betweenthe conductive polyimide 632 and the titanium ferrule 618. In this casethe gold brazes 628 and 630 are shown on the opposite side away from thefeedthrough capacitor 600. Accordingly, there is no way in thisstructure for the feedthrough capacitor ground polyimide connection tohave contact with the gold braze 630. Thus, this prior art assembly issubject to EMI filter performance degradation if the oxide layer becomestoo thick. Product life is another concern. Oxides can build up veryslowly over time and lead to a latent type of design defect.

FIG. 28 illustrates the novel technology of the present invention asapplied to the basic structures illustrated in FIGS. 26 and 27. Theunique Ableloc 5500 or equivalent high temperature thermal plasticpolyimide supportive tape 748 allows the nonconductive insulatingmaterial to be held in place as shown (B staged epoxy washers could alsobe used, however, their temperature rating is not as high). This allowsclear access for the conductive polyimide 744 or 732 to penetrate andcontact the gold braze area 746. In this case, it is important that thegold braze be on the capacitor side of the insulator 724. The assemblyshown in FIG. 28 no longer requires that the pin(s) 716 be restrictedsolely to platinum iridium or other non-oxidizing materials. This allowsthe use of much lower cost niobium or tantalum pins. The electricalconnection can be between the capacitor inside diameter metallization710 directly to the gold braze 728 itself. Accordingly, there is no needfor an electrical connection between the capacitor inside diametermetallization 710 and the lead wire 716 at all. It can also be clearlyseen in FIG. 28 that it would not matter if the inside diameter of theferrule 718 was heavily oxidized. This is because there is an electricalconnection directly from the capacitor outside diameter metallization714 to the outside diameter gold braze 730.

FIG. 29 is a broken out enlarged view of the outside diameter connectionof FIG. 28. As one can see, there is an oxide layer 734 which would tendto insulate the conductive polyimide or solder 732 from the titanium.However, because of the proper location of insulative material 748, theconductive polyimide, solder or the like 732 can make direct contactbetween the capacitor metallization 714 and the gold braze area 730.Sputtering 754 of metals on the alumina insulator 724 are requiredbefore the gold braze hermetic seal typically can be formed. This allowsthe gold braze material 730 to wet to the alumina insulator 724 and forma hermetic seal.

FIG. 30 is an enlarged view of the electrical connection to the leadwire 716 of FIG. 28. It is assumed that a type of lead wire is used,such as tantalum or niobium, which would be heavily oxidized 734. Notonly are these oxides highly insulative, but they also do not form asolderable surface. However, a feature of the invention is that duringhermetic seal construction, the oxides are absorbed by the metallurgicalbond formed between the gold braze area 728 and the pin 716. This is thesame gold braze that forms the hermetic seal to the alumina insulator724. A sputtered layer 754 allows the gold to wet to the insulator 724.As one can see, no direct connection between the capacitor metallization710 and the lead wire 716 is required. Instead, the connection to thecapacitor is accomplished by the thermalsetting conductive adhesive orsolder 744 which connects from the capacitor metallization 710 directlyto the gold braze 728. Since the gold braze 728 has a metallurgical lowresistance and low impedance connection to the pin, no furtherconnection is required. In the case of a non-oxidizing pin material suchas platinum, gold or platinum-iridium alloy, it is not necessary to formthe structure as illustrated in FIG. 30. In other words, the insulativewasher 748 could extend all the way across the inside diameter therebyblocking access to the gold braze.

The most critical element in a medical implant feedthrough design (thatmust remain hermetic throughout it's device service life) is themetal/ceramic interface. Important are the nature of the bond itself andthe sensitivity of the bond integrity to environmental conditionsimposed as a result of the device fabrication process (like installationby laser welding by the pacemaker manufacturer) or as a part ofenvironmental conditions developed while in service (body fluid ishighly corrosive). For a braze-bonded feedthrough, the bond needs todeform in a ductile manner when environmental conditions create stresses(e.g., heating and cooling cycles that develop during device assemblywelding). Typically, metallization and braze material combinationsdevelop alloys that solidify as intermetallics. These intermetallicsoften show only modest ductility prior to failure. If materialcombinations are not judiciously selected and processes are notunderstood and controlled, significant dissolution can occur, andbrittle fracture of the bond, or latent failures (static fatigue) resultcompromising hermetic integrity of the feedthrough.

A unique challenge for formation of the novel bond pads of the presentinvention is that they are formed as an integral part of the hermeticseal joint. This requires a relatively large amount of gold brazematerial (or other noble metal) to be used. In prior art EMI filteredhuman implant hermetic seals, the volume of braze material is by designrelatively small. In the present invention, with the larger volume ofbraze material that is required, higher stresses due to shrinkage andmismatches in the thermal coefficient of expansion (TCE) of the brazematerial become a major design challenge. The biggest concern is theadded stress in tension or shear which is transmitted to the metalliclayer on the alumina hermetic seal/insulator (this layer is what allowsthe braze material to wet to the alumina and form the hermetic seal andis preferably applied by sputtering or equivalent methods).Unfortunately, the TCE of the high alumina content ceramic insulatordoes not match the TCE of any of the noble metal braze materials.Accordingly, for formation of the novel integrated gold hermeticseal/bonding pad as described herein, a unique metallization is requiredto be used in combination with the present invention that has highmalleability and very high adhesion strength to the alumina ceramic andwill also wet well to the braze material. It is a feature of the presentinvention that the preferred metallization on high alumina ceramics forminiature medical implantable device hermetic terminals, istitanium/molybdenum. Titanium is the active layer, and molybdenum is thebarrier layer controlling how much titanium can actually dissolve in thegold. For example, 2-4 microns of titanium can be sputtered followed by2-4 microns of molybdenum. The thickness will be dependent on thedesign, the application, and the subsequent potential environmentalexposures. In this example, the titanium layer provides the interactionwith the glass phases and alumina particle matrix of the ceramic tocreate a hermetic bond. The molybdenum layer protects the titanium layerfrom excessive oxidation prior to brazing and acts as a barrier betweenthe gold braze material and the titanium layer. Without the molybdenumbarrier layer, an excessive length of exposure of the titanium layer tothe molten gold would accelerate the inherent alloying process andeventually lead to de-wetting, then hermetic failure

The titanium/molybdenum metallization in concert with gold braze,therefore, not only provides a sound hermetic bond, but also provides asufficiently ductile materials feedthrough system to sustain secondarydevice assembly processes or environmental conditions that might developstresses while the device is in service.

Other metallization materials that can be used with gold braze materialsinclude but are not limited to titanium, niobium, chromium, zirconium,or vanadium active materials with molybdenum, platinum, palladium,tantalum or tungsten barrier layers in various combinations. Sputteringis one metallization application method. Other methods that might beused include but are not limited to chemical vapor deposition, laser orother physical vapor deposition processes, vacuum evaporation, thickfilm application methods, plating, and so on.

FIGS. 31-36 illustrate an internally grounded bipolar rectangularfeedthrough capacitor 800 as described in U.S. Pat. No. 5,905,627. Thecenter hole is the grounded hole 858 which would connect to thecapacitor internal electrode plates 808. More specifically, thefeedthrough filter capacitor 800 comprises a monolithic, ceramicinternally grounded bipolar feedthrough filter capacitor having threepassageways extending therethrough. The outer two passageways 856 areconfigured to receive therethrough respective conductive terminal pins816′ and 816″, and the internal diameter of the first passageways 856are metallized 810 to form a conductive link between the activeelectrode plates 806. As is well understood in the art, the activeelectrode plates 806 are typically silk-screened onto ceramic platesforming the feedthrough filter capacitor 800. These plates 806 aresurrounded by an insulative ceramic material 804 that need not bemetallized on its exterior surfaces.

Similarly, ground electrode plates 808 are provided within thefeedthrough filter capacitor 800. The inner diameter of the central orsecond passageway 858 through the feedthrough filter capacitor 800 isalso metallized 811 to conductively connect the ground electrode plates808, which comprise the ground plane of the feedthrough filter capacitor800. The second passageway 858 is configured to receive therethrough theground lead 860 which, in this particular embodiment, comprises a groundpin.

With reference to FIG. 32, the terminal pin subassembly comprises aplate-like conductive ferrule 818 having three apertures therethroughthat correspond to the three passageways through the feedthrough filtercapacitor 800. The conductive terminal pins 816′ and 816″ are eachsupported through the outer apertures by means of an insulator 824(which also may be hermetic), and the ground pin 860 is supported withinthe central aperture by a suitable conductor 830 such as gold brazing,solder, an electrically conductive thermalsetting material orwelding/brazing.

The feedthrough filter capacitor 800, as shown, is placed adjacent tothe non-body fluid side of the conductive ferrule 818 and a conductiveattachment is effected between the metallized inner diameter of thefirst and second passageways 856 and 858 through the feedthrough filtercapacitor 800 and the respective terminal pins 816 and ground lead 860.Alternatively, the capacitor 800 could be placed adjacent to the bodyfluid side of the conductive ferrule 818 provided the capacitorcomprises a design incorporating biocompatible materials. In FIG. 35,the conductive connections 844 between the terminal pins 816 and theground lead 860, with the feedthrough filter capacitor 800 may beeffected by any suitable means such as a solder or an electricallyconductive thermalsetting material or brazing. The result is thefeedthrough filter capacitor assembly illustrated in FIGS. 35 and 36which may then be subsequently laser welded into the titanium housing ofan implantable medical device.

FIG. 35 illustrates the internally grounded bipolar feedthroughcapacitor 800 of FIG. 31 mounted to the hermetic feedthrough terminal802 of FIG. 32. The ground lead 860 can be shortened so that it does notprotrude through the capacitor 800 or it can be lengthened depending onwhether or not a circuit attachment is required within the implantablemedical or other electronic device. If the lead wires are solderable(platinum or gold), then the connection between the lead wires and thecapacitor inside diameter metallization can be accomplished usingsolder, conductive adhesive or the like. A feature of the internallygrounded feedthrough capacitor 800 is that no outside diameter (orperimeter in the case of FIG. 35) electrical connection or capacitormetallization is required.

FIG. 36 is a cross-section of the capacitor assembly of FIG. 35. Thisillustrates several novel features of the present invention that areapplicable to the internally grounded feedthrough capacitor, especiallywhen lead wire materials that are subject to oxidation are used (such asniobium or tantalum). As one can see, the thermal plastic polyimidesupportive tape 850 has been carefully punched, die-cut, or laser cut toalign with the capacitor such that the capacitor feedthrough holes areopen to the gold braze material 830 underneath. This allows a directconnection of the solder or conductive polyimide 844 to connect directlybetween the capacitor metallization 810, 811 and gold braze material830. Accordingly, this opens up a wide variety of lead materials foruse, which could not be considered before due to their heavy oxidationor poor solderability properties. This also allows the use of a groundpin of alternate materials, like titanium. A titanium ground pin isdesirable because it is very easy to weld a titanium pin into a titaniumferrule. In the past, it was not possible to solder directly totitanium, however, a feature of the present invention is the capabilityof connection to the gold braze area. It should be apparent that not allleads are required to be constructed of the same material. For example,the center (ground) lead 860 could be titanium and the two active pins816′ and 816″ could be platinum. In this case, it would not be requiredthat conductive material 844 adjacent the platinum pins 816′ and 816″contact the gold braze 830.

FIG. 37 illustrates a novel hybrid capacitor 900 which has thecharacteristics of a conventional surface mounted feedthrough capacitorand an internally grounded capacitor. This capacitor 900 has a groundhole 958 in the center which connects to the internal ground electrodeplates 908 and also has ground terminations 914 at either end. Thereason for this is that this capacitor has a form factor which tends toincrease its inductance and impedance. Accordingly, if one were to onlymake connection to the ground electrodes 908 shown in FIG. 38 at thecenter hole 958, there would be too much inductance between this and theouter pins to perform effective EMI filtering. This hybrid design isbest illustrated by the ground electrode plate pattern as shown in FIG.38, wherein the ground electrode 908 is attached to the titanium ferrule918 at both the right and left ends and also in the middle. Thisguarantees that the capacitor 900 will have very low impedance acrossits entire ground plane thereby ensuring that it will work properly as ahigh frequency EMI filter. FIG. 39 is an illustration of the activeelectrode plate pattern 906.

FIG. 40 illustrates the simplified hermetic terminal 902. The centeredground pin 960 is welded or brazed 928 directly to the ferrule 918. Thisforms a low resistance and low inductance ground connection to the pin960. The other pins 916 are shown in insulative relationship with theferrule 918. The novel gold bond pads of the present invention are shownas 946. Restated, the ground pin 960 has been solidly brazed directly tothe ferrule 918. This provides a very low impedance RF ground betweenthe center pin 960 and the overall electromagnetic shield. One can alsosee in FIG. 40 that the gold bond pads 946 have been added on either endto form a convenient surface for the electrical connection between thecapacitor end terminations 914 and the ferrule 918. It can also be seenthat the other four pins 916 on both the right and left sides of thecapacitor 900 are in electrically insulative relationship. This is donethrough the insulators 924 which can be glass or a gold brazed aluminaseal.

FIG. 41 is a top view of the capacitor of FIG. 37 mounted to titaniumferrule 918. The novel gold braze ground pads 946 of the presentinvention have been added so that an oxide free electrical connectioncan be made between the capacitor-ground terminations 914 and theconductive ferrule 918.

FIG. 42 is a cross-sectional view of the capacitor 900 assembled to thehermetic terminal 902 of FIG. 40. As shown, the gold bond pads 946 arealso part of a single monolithic structure forming the hermetic sealbetween the ferrule 918 and the insulator 924, in the same manner andfor the same reasons as discussed above in connection with FIG. 22. Theconnection between the capacitor ground metallization 914 (at its twoends) and the gold bond pads 946 is shown as material 932, which can besolder, conductive thermalsetting material, or the like. The connectionto the centered ground pin 960 is illustrated by material 944 which canalso be solder, conductive thermalsetting material, or the like. Aspreviously mentioned, in the present invention it is desirable to forminsulative material 948 such that the electrical connecting material 944adjacent to the ground pin 960 will directly contact the gold braze 928.This is particularly important for ground pin lead materials that arenot readily solderable or that form insulative oxide layers. The novelgold bond pad area 946 as previously mentioned could also beaccomplished by sputtering, plating and the like.

As illustrated in FIG. 42, for comparison purposes, the hermeticterminal 902 includes two distinctly different sets of lead wires 916.To the left of the ground pin 960, the lead wires 916 are shown ascomprised of low cost niobium or tantalum pins on which heavy oxidestypically form. When utilizing such low cost pins, the pads of oxideresistant conductive biostable material, noble metal, or the like, 946are utilized to provide both a hermetic seal between the pins and theinsulator 924, and also to provide a reliable electrical connectionbetween the interior termination surfaces 910 and the leads 916, asdiscussed above in connection with FIGS. 24, 28-30 and 36. In contrast,the lead wires 916 to the right of the ground pin 960 are all platinum.As a noble metal, platinum is not subject to oxidation. Accordingly, itis not necessary for the solder or conductive polyimide used to connectbetween the capacitor inside diameter metallization and the lead wire toalso contact the gold braze material 928. In other words, an oxide freeelectrical connection has already been made between the capacitor insidediameter metallization 910 and the lead wire 916, therefore it is notnecessary to modify this assembly to contact the gold braze. However, inaccordance with the invention, the aforementioned polyimide supportivetape 948 or the like could be placed to allow direct contact from theground pin 960 to the gold braze 930 thereby allowing the use of aground lead wire such as titanium, niobium or tantalum.

FIG. 43 shows a hybrid capacitor 1000 which has a centered ground pin1060 and, because of its length and the desire to reduce inductance, isalso grounded at its right and left ends using conductive polyimide 1032to the gold bond pads 1046. This is a hybrid in that it incorporates thefeatures of both U.S. Pat. Nos. 5,333,905 and 5,095,627. FIG. 43illustrates novel wire bond pads that overcome all of the obviousdeficiencies of the aforementioned Wolf patent. The preferred locationfor the hermetic braze between the insulators 1024 and the hermeticterminal 1002 is at the pads 1046. This takes the gold braze away fromthe body fluid both at each terminal pin and also at the hermetic sealjoint to the ferrule. When a header block, which is commonly used in theindustry is attached, silicone or other material is utilized which willfill the space between the lead all the way down to the gold braze. Thiseffectively blocks the ready access of body fluids to the gold brazethereby preventing reverse electroplating involving material depositionto some other surface in the presence of a voltage bias. In other words,the location of the hermetic seal shown in FIG. 43 will overcome anyproblem with long term exposure to body fluid.

FIGS. 43 and 44 further illustrate an extruded nail head lead 1016 ofbio-compatible material such as a noble metal including platinum,platinum iridium, gold and the like. The nail head portion 1062 of thelead 1016 on the bottom or body fluid side could be extruded as onepiece particularly with a malleable material welded in place, brazed inplace, or adhesively secured in place to the lead 1016. The capacitor1000 is attached to the terminal 1002 using similar processes asdescribed above, and the leads 1016 are attached at the time that thehermetic seal joint 1046 is formed. During capacitor attachment theleads 1016 are allowed to stick through the capacitor 1000 as shown. Atthis point there are a number of options for the assembly. One optionwould be to make a solder joint, braze, weld or a thermalsettingconductive adhesive joint 1099 between the capacitor inside diametertermination and the nail head terminal pin 1016. One could then add awire bond closed pad or cap 1064 and attach it by soldering, welding,thermal conductive adhesive brazing or the like 1098. The wire bond pad1064 does not need to be bio-compatible and could be made of a number ofinexpensive materials including nickel, copper, steel and the like. Forwire bond applications it is usually required that the wire bond pad1064 be pure (soft) gold plated, but a number of other surface finishescan be applied as well. The wire bond pads/nail head assembly 1016, 1064could also be formed from the group of metals including: tantalum,molybdenum, titanium, rhodium, titanium alloys, osmium, silver andsilver alloys, vanadium, platinum, niobium, platinum alloys, stainlesssteel, tungsten, rhenium, zirconium, vanadium and ruthenium.

FIG. 45 illustrates an internally grounded hex polar capacitor 1100embodying the invention (refer to U.S. Pat. No. 5,905,627). In thisparticular device, the novel wire bond pads 1164 as previously describedhave been utilized. The nail head pin 1116 is of the same group ofmaterials as previously described for FIG. 43. However, in thisembodiment the hermetic seal 1146 has been moved to an alternatelocation and is now closer to exposure to body fluids. This is alsoacceptable to many customers but is not the preferred embodiment formaximum resistance to long term decomposition by metal migration.

The wire bond pad 1164 on the inside of the implantable medical devicehas also been modified so it has an open hole. In this case this a ringstructure which is slipped over the bio-compatible pin 1116 and thenattached by soldering, welding, brazing, or thermalsetting conductiveadhesive or the like. An advantage of this structure is it is a littlebit easier to assemble and inspect. A disadvantage is that the areaavailable for customer attachment of their lead wires by ultrasonic wirebonding, thermal sonic welding or direct welding has been reduced. Inother words there is less flat surface area available for customer leadattach.

Referring to FIG. 47A, a different embodiment of attachment of the leadwire 1160 is shown. In this case the lead wire 1160 extends through atoroidal ring 1164′ which may be constructed of various materials fromthe group of metals, and ceramics. One preferred embodiment would be theuse of alumina ceramic which was metallized. This would allow one toform the electrical connection shown while at the same time allowing thelead wire 1160 to protrude through. In this case the very end of thelead wire 1160 could be the wire bond pad itself. There are a number ofsupplementary processes available after the extrusion of this lead wireto provide a flat and parallel surface. This has a number of advantagesthat will be obvious to one skilled in the art including the ability toreadily inspect the joints.

More particularly, the preferred metallized alumina toroidal ring 1164′has been metallized on all surfaces so it is both solderable andconductive. Solder, thermalsetting conductive adhesive, welding or thelike 1168 performs an electrical connection between the circular torroid1164′ which in turn connects to the capacitor 1100 active electrodeplates 1106. In addition, material 1170, which can be of the group ofsolder, thermalsetting conductive adhesives, welding, brazes or thelike, forms the electrical connection between the lead wire 1160 to thetorroidal structure 1164′ which then couples through the electricalconnection 1168 via the capacitor metallization 1110 to the electrodeplates. As shown the tip of the lead wire 1172 is flat to accept leadattachment by the customer by wire bonding, thermal sonic bonding, laserwelding or the like. A supplementary nail head or enlarged area could beadded to the tip 1172 to increase the surface area available for suchcustomer lead attachment operations. One particular advantage of thestructure shown in FIG. 47 is the ability to select a material thatclosely matches a thermal co-efficient expansion of the ceramiccapacitor 1100. Such materials include fosterite, zirconium, goldalloys, or materials such dumet.

Capacitor 1100 has inside diameter metallization 1197 at each of theseven inside diameters to make electrical connection to the ground andactive electrode plate sets. This metallization also appears on top ofthe capacitor as a circular mounting/bonding pad 1199. In this case,there is no need to fill the space between the capacitor insidediameters and the noble metal lead wires with an electrical connectionmaterial.

FIG. 47B shows that the lead wire and its electrical connection may besubflush or below the top of the ring pad 1164. In this case, the ringpad forms the wire bond surface.

As shown in FIG. 47C, the electrical connection is formed between pin1116 and the capacitor top metallization 1199 using solder, braze,conductive adhesive or the like. Alternative connections using a varietyof wire bond pad end caps are shown in FIGS. 47A, 47B, and 47C.

FIGS. 48 and 49 show an externally grounded quadpolar device. While acompatible nail head pin 1216 is utilized and in this case, the hermeticseal connection 1246 between the alumina ceramic 1224 and the nail headpin 1216 is in the preferred location. Drawing attention now to the wirebond end cap 1264, a different attachment method is contemplated. Thisattachment method is desirable in that it completely eliminates thenecessity for any contact materials or any solder or other materials tobe placed between the lead wire 1216 and the inside diameter terminationof the ceramic capacitor 1200. In this case the capacitor 1200 insidediameter metallization 1210 is also formed as a circular structure onthe top surfaces of the ceramic capacitor. This is commonly used in theconnector industry and with planar arrays. Such structures are normallyprinted on the top surface of the ceramic capacitor by silk screeningprocesses or the like. Accordingly, it is easy to form this on the topsurface of the capacitor 1200. This makes the attachment of the end cap1264 very simple and easy to facilitate in a manufacturing operation. Asbest seen in FIG. 49, attachment of the wire bond cap 1264 is simplyaccomplished by making a solder joint, conductive thermalsettingadhesive joint, braze joint, weld joint or the like shown as 1266. Thismakes a direct connection to the capacitor termination 1210.Accordingly, there is no other connection to the capacitor insidediameter that is needed. At the same time that the joint 1266 is formedor at a different time, the electrical connection 1299 to the end cap1264 is also made. As previously mentioned, this can be donethermalsetting conductive adhesives, solder, brazes, welds or the like.

This is a major advantage over the aforementioned Wolf patent in thatthe inside diameter of the capacitor does not have any materials thatmis-match it in its thermal co-efficient of expansion. Accordingly, thecapacitor will be mechanically more rugged and more resistant to thermalshock such as those induced by the customer during installation by laserwelding. The capacitor termination materials are preferably in this caseformed from either plating or a fired on silver or a palladium-silverglass frit. These are put on as a thick film process sufficient so thatit forms a mechanically rugged and electrically reliable attachment tothe capacitor active electrode plates 1206.

Although several embodiments of the invention have been described indetail for purposes of illustration, various modifications of each maybe made without departing from the spirit and scope of the invention.Accordingly, the invention is not to be limited, except as by theappended claims.

What is claimed:
 1. An EMI feedthrough filter terminal assembly,comprising: a feedthrough filter capacitor including first and secondsets of electrode plates, a passageway therethrough having a firsttermination surface conductively coupling the first set of electrodeplates, and a second termination surface exteriorly coupling the secondset of electrode plates; a conductive ferrule adjacent to thefeedthrough filter capacitor; at least one conductive terminal pinextending through the passageway in conductive relation with the firstset of electrode plates, and through the ferrule in non-conductiverelation; an insulator fixed to the ferrule for conductively isolatingthe terminal pin from the ferrule; and an oxide resistant conductivehermetic seal between the insulator and the ferrule, the oxide resistantconductive seal including an oxide resistant conductive pad on a surfaceof the ferrule conductively coupled to the second termination surface.2. The terminal assembly of claim 1, including a conductive connectorextending between the second termination surface and the oxide resistantconductive pad.
 3. The terminal assembly of claim 2, wherein theconductive connector is taken from the group consisting of conductivepolyimide, solder, weld or braze.
 4. The terminal assembly of claim 1,wherein the oxide resistant conductive pad comprises a noble metal. 5.The terminal assembly of claim 4, wherein the noble metal is taken fromthe group consisting of gold, platinum, and oxide resistant alloysthereof.
 6. The terminal assembly of claim 1, wherein the secondtermination surface comprises a plurality of second termination surfacesand wherein the oxide resistant conductive pad includes a correspondingplurality of pads conductively coupled to the plurality of secondtermination surfaces.
 7. The terminal assembly of claim 1, includingmeans for hermetically sealing passage of the terminal pin through theferrule.
 8. The terminal assembly of claim 1, wherein the ferrule andthe insulator comprise a pre-fabricated hermetic terminal pinsub-assembly.
 9. The terminal assembly of claim 1, wherein the firstpassageway through the feedthrough filter capacitor comprises aplurality of first passageways each having a distinct first terminationsurface conductively coupled to a distinct first set of electrodeplates, and wherein the at least one conductive terminal pin comprises aterminal pin extending through each of the plurality of firstpassageways.
 10. The terminal assembly of claim 1, including aninsulative washer disposed between the feedthrough filter capacitor andthe insulator.
 11. The terminal assembly of claim 10, wherein theinsulative washer comprises a thermal plastic polyimide supported tape.12. The terminal assembly of claim 11, wherein the thermal plasticpolyimide supported tape comprises Ableloc.
 13. The terminal assembly ofclaim 10, wherein the washer includes a gap adjacent to the terminalpin.
 14. The terminal assembly of claim 1, including a second oxideresistant conductive pad conductively attached to the at least oneterminal pin, and means for conductively coupling the second oxideresistant conductive pad to the first termination surface independentlyof the terminal pin.
 15. The terminal assembly of claim 14, wherein thesecond oxide resistant conductive pad comprises a noble metal.
 16. Theterminal assembly of claim 1, specifically constructed for medicalimplant applications.
 17. The terminal assembly of claim 16, wherein themedical implant applications include cardiac pacemakers, implantablecardioverter defibrillators, cochlear implants, neuro-stimulators,internal drug pumps, bone growth stimulators, artificial organs,artificial hearts, hearing assist stimulators, artificial limbs,artificial eyes, muscle actuators, and deep brain stimulators forseizure control, pain management and gene therapy.
 18. The terminalassembly of claim 1, wherein the oxide resistant conductive pad isapplied through a soldering process.
 19. The terminal assembly of claim1, wherein the oxide resistant conductive pad is applied through aphysical vapor deposition process.
 20. The terminal assembly of claim 1,wherein the oxide resistant conductive pad is applied through anelectroplating process.
 21. The terminal assembly of claim 1, whereinthe oxide resistant conductive pad is applied through a plasma arcdeposition process.
 22. The terminal assembly of claim 1, wherein theoxide resistant conductive pad is applied through an ion beam process.23. The terminal assembly of claim 1, wherein the oxide resistantconductive pad is applied through a chemical vapor deposition process.24. The terminal assembly of claim 1, wherein the oxide resistantconductive pad is applied through a laser ablation process.
 25. Theterminal assembly of claim 1, wherein the oxide resistant conductive padcomprises a gold braze.
 26. The terminal assembly of claim 25, whereinthe oxide resistant conductive pad is attached, at least in part, to atitanium/molybdenum surface.
 27. The terminal assembly of claim 1,wherein the terminal pin comprises an integral oxide resistant biostablewire bond pad on a body fluid side of the terminal assembly.
 28. Theterminal assembly of claim 27, wherein the wire bond pad comprises anoble metal.
 29. The terminal assembly of claim 28, wherein the noblemetal is taken from the group consisting of gold, platinum, and oxideresistant alloys thereof.
 30. The terminal assembly of claim 27,including a mating wire bond cap attached to the terminal pin oppositethe wire bond pad.
 31. The terminal assembly of claim 30, wherein thewire bond cap comprises a material taken from the group consisting oftantalum, molybdenum, titanium, rhodium, titanium alloys, osmium, silverand silver alloys, vanadium, platinum, niobium, platinum alloys,stainless steel, tungsten, rhenium, zirconium, vanadium and ruthenium.32. An EMI feedthrough filter terminal assembly, comprising: afeedthrough filter capacitor including first and second sets ofelectrode plates, a passageway therethrough having a first terminationsurface conductively coupling the first set of electrode plates, and aplurality of second termination surfaces exteriorly coupling the secondset of electrode plates; a conductive ferrule adjacent to thefeedthrough filter capacitor; at least one conductive terminal pinextending through the passageway in conductive relation with the firstset of electrode plates, and through the ferrule in non-conductiverelation; an insulator fixed to the ferrule for conductively isolatingthe terminal pin from the ferrule; an oxide resistant hermetic sealbetween the insulator and the ferrule, the hermetic seal including aplurality of conductive pads of oxide resistant biostable material, on asurface of the ferrule conductively coupled to the plurality of secondtermination surfaces; and conductive connectors extending between therespective second termination surfaces and the conductive pads.
 33. Theterminal assembly of claim 32, including means for hermetically sealingpassage of the terminal pin through the ferrule.
 34. The terminalassembly of claim 32, wherein the ferrule and the insulator comprise apre-fabricated hermetic terminal pin sub-assembly.
 35. The terminalassembly of claim 32, wherein the first passageway through thefeedthrough filter capacitor comprises a plurality of first passagewayseach having a distinct first termination surface conductively coupled toa distinct first set of electrode plates, and wherein the at least oneconductive terminal pin comprises a terminal pin extending through eachof the plurality of first passageways.
 36. The terminal assembly ofclaim 32, including an insulative washer disposed between thefeedthrough filter capacitor and the insulator.
 37. The terminalassembly of claim 36, wherein the insulative washer comprises a thermalplastic polyimide supported tape.
 38. The terminal assembly of claim 37,wherein the thermal plastic polyimide supported tape comprises Ableloc.39. The terminal assembly of claim 36, wherein the washer includes a gapadjacent to the terminal pin.
 40. The terminal assembly of claim 32,including a second conductive pad of oxide resistant biostable materialconductively attached to the at least one terminal pin, and means forconductively coupling the second pad to the first termination surfaceindependently of the terminal pin.
 41. The terminal assembly of claim40, wherein the conductive pads comprise a noble metal.
 42. The terminalassembly of claim 41, wherein the noble metal is taken from the groupconsisting of gold, platinum, and oxide resistant alloys thereof. 43.The terminal assembly of claim 40, wherein the conductive pads comprisea material taken from the group consisting of tantalum, molybdenum,titanium, rhodium, titanium alloys, osmium, silver and silver alloys,vanadium, platinum, niobium, platinum alloys, stainless steel, tungsten,rhenium, zirconium, vanadium and ruthenium.
 44. The terminal assembly ofclaim 32, specifically constructed for medical implant applications. 45.The terminal assembly of claim 44, wherein the medical implantapplications include cardiac pacemakers, implantable cardioverterdefibrillators, cochlear implants, neuro-stimulators, internal drugpumps, bone growth stimulators, artificial organs, artificial hearts,hearing assist stimulators, artificial limbs, artificial eyes, muscleactuators, and deep brain stimulators for seizure control, painmanagement, and gene therapy.
 46. The terminal assembly of claim 32,wherein the oxide resistant conductive pad comprises a gold braze. 47.The terminal assembly of claim 46, wherein the terminal pin comprises anintegral oxide resistant biostable wire bond pad on a body fluid side ofthe terminal assembly.
 48. The terminal assembly of claim 32, whereinthe terminal pin comprises an integral oxide resistant biostable wirebond pad on a body fluid side of the terminal assembly.
 49. The terminalassembly of 48, wherein the wire bond pad comprises a noble metal. 50.The terminal assembly of claim 49, wherein the noble metal is taken fromthe group consisting of gold, platinum, and oxide resistant alloysthereof.
 51. The terminal assembly of claim 48, including a mating wirebond cap attached to the terminal pin opposite the wire bond pad. 52.The terminal assembly of claim 51, wherein the wire bond cap comprises amaterial taken from the group consisting of tantalum, molybdenum,titanium, rhodium, titanium alloys, osmium, silver and silver alloys,vanadium, platinum, niobium, platinum alloys, stainless steel, tungsten,rhenium, zirconium, vanadium and ruthenium.
 53. An EMI feedthroughfilter terminal assembly for use in medical implant applications,comprising: a feedthrough filter capacitor including first and secondsets of electrode plates, a plurality of passageways therethrough eachhaving a distinct first termination surface conductively coupled to adistinct first set of electrode plates, and a plurality of secondtermination surfaces exteriorly coupling the second set of electrodeplates; a conductive ferrule adjacent to the feedthrough filtercapacitor; a plurality of terminal pins corresponding with the number ofpassageways through the feedthrough filter capacitor, each terminal pinextending through a respective passageway in conductive relation withthe corresponding distinct first set of electrode plates, and throughthe ferrule in non-conductive relation; an insulator fixed to theferrule for conductively isolating the terminal pins from the ferrule,wherein the ferrule and the insulator comprise a pre-fabricated hermeticterminal pin sub-assembly; an oxide resistant hermetic seal between theinsulator and the ferrule, the hermetic seal including a plurality ofconductive pads of oxide resistant biostable material on a surface ofthe ferrule conductively coupled to the plurality of second terminationsurfaces; and conductive connectors extending between each of therespective second termination surfaces and conductive pads.
 54. Theterminal assembly of claim 53, including an insulative washer disposedbetween the feedthrough filter capacitor and the insulator.
 55. Theterminal assembly of claim 54, wherein the insulative washer comprises athermal plastic polyimide supported tape.
 56. The terminal assembly ofclaim 55, wherein the thermal plastic polyimide supported tape comprisesAbleloc.
 57. The terminal assembly of claim 53, including a secondconductive pad of oxide resistant biostable material conductivelyattached to the at least one terminal pin, and means for conductivelycoupling the second conductive pad to the first termination surfaceindependently of the terminal pin.
 58. The terminal assembly of claim57, wherein the conductive pads comprise a noble metal.
 59. The terminalassembly of claim 58, wherein the noble metal is taken from the groupconsisting of gold, platinum, and oxide resistant alloys thereof. 60.The terminal assembly of claim 57, wherein the conductive pads comprisea material taken from the group consisting of tantalum, molybdenum,titanium, rhodium, titanium alloys, osmium, silver and silver alloys,vanadium, platinum, niobium, platinum alloys, stainless steel, tungsten,rhenium, zirconium, vanadium and ruthenium.
 61. The terminal assembly ofclaim 53, including means for hermetically sealing passage of theterminal pin through the ferrule.
 62. The terminal assembly of claim 53,wherein the medical implant applications include cardiac pacemakers,implantable cardioverter defibrillators, cochlear implants,neuro-stimulators, internal drug pumps, bone growth stimulators,artificial organs, artificial hearts, hearing assist stimulators,artificial limbs, artificial eyes, muscle actuators and deep brainstimulators for seizure control, pain management, and gene therapy. 63.The terminal assembly of claim 53, wherein the oxide resistantconductive pad comprises a gold braze attached, at least in part, to atitanium/molybdenum surface.
 64. The terminal assembly of claim 53,wherein the oxide resistant conductive pad is applied through any one ofthe following: a soldering process, a physical vapor deposition process,an electroplating process, a plasma arc deposition process, an ion beamprocess, a chemical vapor deposition process, or a laser ablationprocess.
 65. The terminal assembly of claim 53, wherein the terminalpins each comprise an integral oxide resistant biostable wire bond padon a body fluid side of the terminal assembly.
 66. The terminal assemblyof claim 65, wherein the wire bond pad comprises a noble metal.
 67. Theterminal assembly of claim 66, wherein the noble metal is taken from thegroup consisting of gold, platinum, and oxide resistant alloys thereof.68. The terminal assembly of claim 65, including a mating wire bond capattached to each terminal pin opposite the wire bond pad.
 69. Theterminal assembly of claim 68, wherein the wire bond cap comprises amaterial taken from the group consisting of tantalum, molybdenum,titanium, rhodium, titanium alloys, osmium, silver and silver alloys,vanadium, platinum, niobium, platinum alloys, stainless steel, tungsten,rhenium, zirconium, vanadium and ruthenium.